1. Field of the Invention
The invention relates to a network diagnostic method, and in particular relates to a Gigabit Ethernet network diagnostic method.
2. Description of the Related Art
Computer network transmission lines can be destroyed by a variety of causes, for example, oxidation, humidity, excavation, or other unknown causes resulting in various conditions, such as, a cable open, a cable short, and an impedance mismatch. A cable open exists when a lack of continuity occurs between the pins at each end of the cable. A cable short occurs when two or more conductors short circuits. When two metallic conductors are placed close together, the characteristic impedance of a transmission line (cable) occurs. A correctly terminated line is defined that both the source impedance and the load impedance are equal to the characteristic impedance of a transmission line (cable). For a perfectly terminated line, the reflected wave is zero. In this case, the destination (load) absorbs all the energy of the source wave. However, an impedance mismatch occurs when either the source impedance or the load impedance differs from the characteristic impedance of the transmission line (cable).
Time Domain Reflectometry (TDR), similar to the principle of the radar, is the analysis of a conductor (wire, cable, or optical fiber) by sending a pulsed signal into the conductor, and then examining the reflection of the pulsed signal. When the transmitted pulse reaches the end of the cable, or a fault along the cable, part or all of the pulse energy is reflected back to the source. By examining the polarity, amplitude, frequencies, or other electrical signatures of all reflections, tampering or bugs may be precisely located. Accordingly, TDR technology can be utilized to remotely and non-evasively locate and identify cabling problems such as cable opens, cable shorts, or any impedance mismatches. Any wire with fault will cause a detectable anomaly, and the technician will then perform a physical inspection at the location of the anomaly.
FIG. 1a to FIG. 1d illustrate various cable conditions that can be diagnosed by Time Domain Reflectometry (TDR).
FIG. 1a illustrates a source wave and its corresponding reflected wave in a cable open condition in accordance with TDR. As shown in FIG. 1a, a source wave 11 with amplitude As is sent and a reflected wave 12 with an amplitude Ar1 is received after a period of time Tr. The reflected wave 12 is identical to the source wave 11, since the load impedance is regarded as infinite and the load reflects all the energy of the source wave. Accordingly, the reflected wave 12 has the same amplitude and polarity as the source wave 11.
FIG. 1b illustrates a source wave and its corresponding reflected wave in a cable short condition in accordance with TDR. As shown in FIG. 1b, a source wave 13 with amplitude As is sent and a reflected wave 14 with an amplitude Ar2 is received after a period of time Tr. The magnitude of the amplitude Ar2 of the reflected wave 14 is equal to that of the source wave 13, i.e., As, while the polarities of the reflected wave 14 and the source wave 13 are opposite.
FIG. 1c illustrates a source wave and its corresponding reflected wave when the load impedance is greater than the source impedance in accordance with TDR. As shown in FIG. 1c, a source wave 15 with amplitude As is sent and a reflected wave 16 with an amplitude Ar3 is received after a period of time Tr. The magnitude of the amplitude Ar3 of the reflected wave 16 is below that of the source wave 15, i.e., As, and the polarities of the reflected wave 16 and the source wave 15 are the same.
FIG. 1d illustrates a source wave and its corresponding reflected wave when the load impedance is below the source impedance in accordance with TDR. As shown in FIG. 1d, a source wave 17 with amplitude As is sent and a reflected wave 18 with an amplitude Ar4 is received after a period of time Tr. The magnitude of the amplitude Ar4 of the reflected wave 18 is below that of the source wave 17, i.e., As, and the polarities of the reflected wave 18 and the source wave 17 are opposite.